What is a plantar wart?

What is a Plantar Wart?

A plantar wart (verruca plantaris) is a benign skin lesion on the sole of the foot caused by human papillomavirus (HPV) infection of keratinocytes, resulting in epidermal thickening and hyperkeratinization that develops weeks to months after initial infection. 1, 2

Causative Agent and Pathophysiology

• HPV types 1,2,4,27, and 57 are responsible for most plantar warts, with HPV-1 and HPV-2 being the most common causative agents 2
• The virus infects keratinocytes at the basal layer of the epidermis, leading to clonal proliferation that eventually produces a visible wart 1
• HPV requires an epidermal abrasion and transiently impaired immune function to successfully inoculate a keratinocyte 3

Clinical Characteristics and Diagnosis

The diagnosis is typically straightforward and can be confirmed by paring down the lesion:

• Pinpoint bleeding occurs when paring exposes the capillary loops of elongated dermal papillae—this is the hallmark diagnostic feature 1, 2
• Plantar warts appear as thick, endophytic, hyperkeratotic lesions with disrupted or absent skin lines across the surface 4, 5
• Multiple "seeds" (thrombosed vessels) may be visible in the dermis after debridement 5

Key Differential Diagnosis

Plantar warts must be distinguished from:

• Corns: Show a translucent central core without pinpoint bleeding 4
• Calluses: Display uniform opacity without bleeding and intact skin lines 4
• Other keratotic lesions such as actinic keratoses, squamous cell carcinoma, or focal palmoplantar keratoderma 1

Transmission and Epidemiology

• HPV spreads through direct contact or environmental exposure, with the virus potentially remaining infectious outside the body for months or years 1, 2
• Plantar warts affect up to 33% of children and 3.5% of adults 6
• Athletes and populations with frequent barefoot exposure in communal areas face increased risk 7

Natural History

The natural course varies significantly by age:

• In children: 50% clear spontaneously within 1 year, and two-thirds by 2 years 1, 4
• In adults: Warts are much more persistent, often lasting 5-10 years without treatment 1
• Spontaneous clearance begins with reduction in wart size followed by complete disappearance 1

Clinical Significance and Red Flags

• Plantar warts can cause pain and functional impairment depending on their size and location 1, 7
• Unusually severe or prolonged warts should prompt consideration of underlying immune deficiency, including lymphoma, idiopathic CD4 lymphocytopenia, or HIV infection 1, 4
• In immunosuppressed patients, warts may be large, extensive, and highly resistant to treatment 1

Management Principles

For immunocompetent patients with asymptomatic warts, expectant management is entirely acceptable 1, 4

When treatment is indicated:

• First-line: Salicylic acid 15-40% topical preparations applied after debridement, which promote exfoliation of epidermal cells 2, 4
• Alternative: Cryotherapy with liquid nitrogen 2, 4
• Treatment should be guided by patient preference, lesion characteristics, and provider experience, as no single treatment is ideal for all patients 2

Common Pitfall

Plantar warts are frequently mistaken for calluses in athletes and other active populations, leading to misdiagnosis and delayed appropriate treatment 5. Always pare down suspicious hyperkeratotic lesions to look for the characteristic pinpoint bleeding pattern.